Biocides have been useful in various coating and paint formulations, such as house paints, to prevent the growth of microorganisms such as bacteria, mold, and mildew. However, certain biocides can undergo undesirable photochemical reactions upon exposure to ultraviolet (UV) radiation. This poses a problem especially for water-based exterior house paints, which are exposed to sunlight.
Halogenated benzonitrile-based biocides, such as chlorothalonil, are effective at suppressing the growth of fungi, but, when used in paints, present a problem of fading of colored paints upon exposure to UV radiation. The fading is believed to be related to degradation of the binder, which produces chalking. Although the chalking can occur in light as well as dark colored paints, it is especially noticeable with dark or deeply hued pigments such as blacks and blues. This problem precludes the use of halogenated benzonitrile based-biocides in such paints.
U.S. Pat. No. 6,409,809 describes a coating composition of a halogenated benzonitrile, such as chlorothalonil, in combination with a conazole compound. While effective at reducing the fading of colored paints, the coating compositions described therein are economically prohibitive to make and sell to the consumer.
There thus remains a need to provide a biocide composition of a halogenated benzonitrile, such as chlorothalonil, for use in coating materials, such as paints, which composition will effectively address the problem of fading of colored paints upon exposure to light, without significantly raising the costs of such paints to the consumer.